Light source module and method for production thereof

ABSTRACT

A light source module having a plurality of LEDs connected to a metal carrier ( 4 ) by means of an insulating layer ( 3 ). In order to afford protection against mechanical effects and in order to form a reflector, the LEDs are surrounded by a frame ( 10 ), which is segmented into a plurality of parts by expansion joints ( 13 ), in order that stresses occurring as a result of temperature fluctuations are absorbed.

RELATED APPLICATIONS

This is a U.S. national stage of application Ser. No. PCT/DE03/003189,filed on 24 Sept. 2003.

This patent application claims the priority of German patent applicationno. 10245945.2filed 30 Sept. 2002, the disclosure content of which ishereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to a light source module having a plurality ofLEDs (LED=light emitting device) connected to a metal carrier in aninsulating manner.

BACKGROUND OF THE INVENTION

A light source module of this type is described e.g. in the publishedU.S. patent application No. 2003/01788627.

Published U.S. patent application No. 2004/0089898 discloses e.g.arranging an LED in a frame and potting the region between frame and LEDwith potting composition. In order to obtain a reflector, preferablyreflective potting composition is first filled into the region betweenframe and LED and subsequently complete potting is effected using clearpotting composition.

This manner of producing a light source module functions without anyproblems if only one LED is arranged within the frame.

However, if a plurality of LEDs are arranged in a frame, the frame iscompletely areally connected by the potting composition to the metalcarrier on which the LEDs are arranged by means of an insulating layer.

In the event of greatly different temperature loads, the metal carrierexpands differently with respect to the frame since the frame isgenerally not composed of metal and, consequently, the two materialshave different coefficients of expansion.

The different coefficients of expansion of these two components meanthat the LEDs are subjected to loading, which can consequently lead tofailures of individual LEDs or in this way to the destruction of theentire light source module.

SUMMARY OF THE INVENTION

One object of the invention is to provide a light source module whichwithstands even greatly varying temperature conditions.

This and other objects are attained in accordance with one aspect of theinvention by virtue of the fact that the LEDs are surrounded by a frame,a potting composition is arranged between the frame and the LEDs, andthe frame has expansion joints.

By introducing the expansion joints into the frame, it is possible touse the technology disclosed in the above-mentioned published U.S.patent application no. 2004/0089898, namely the technology of placing aframe onto the LEDs and potting the interspace with potting composition.

The expansion joints may be realized either by means of portions whichare kept extremely thin in the frame and can deform in the event ofexpansion, or else by means of slots extending completely through theframe.

The frame can be segmented into a plurality of frame parts by expansionjoints.

In this case, a frame part can have a maximum of four cutouts in whichLEDs can be arranged. In the case where the frame is produced fromplastic and the metal carrier is produced from aluminum, this number ofcutouts per frame part guarantees a high reliability and functionalityeven in the event of high temperature fluctuations.

The LEDs can be arranged in the light source module in a grid, e.g. in agrid of 4.5 mm in eight columns and four rows, and may be used forrealizing an LED light source for an HUD system (HUD=Head-up Display) ina motor vehicle.

The segmentation of the frame for producing the light source module ispreferably effected at the end of the process chain, i.e. afterintroduction in the potting composition. This may be done e.g. by meansof a sawing device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a part of the light source module according to theinvention in sectional view,

FIG. 2 shows a frame for the light source module in the view from above,

FIG. 3 shows the section A-A from FIG. 2,

FIGS. 4A and 4B show the frame for the light source module in the viewfrom above and in side view,

FIGS. 5A and 5B show a carrier with applied printed circuit board forthe light source module in the view from above and also in side view,and

FIGS. 6A and 6B show the frame from FIGS. 4 a and 4 b and also thecarrier with applied printed circuit board from FIGS. 5 a and 5 b in themounted state.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an LED light source module in partial sectional view.

In the detail illustrated, the light source module has two LEDs, one LEDin each case comprising two optoelectronic components 1 arranged on acarrier substrate 2.

The carrier substrate 2 is composed of a material exhibiting goodthermal conductivity and it includes an interposed insulating layer 3and also a carrier layer 5 on a metal carrier 4, which serves not onlyas a carrier but also as a heat sink. The metal carrier 4 is preferablycomposed of aluminum or copper in order to obtain a high dissipation ofheat.

The insulating layer 3 integrated in the carrier substrate 2 generallycomprises a silicon oxide layer 6 and a silicon nitride layer 7 appliedon the silicon oxide layer 6. The silicon oxide layer is applied on acarrier layer 5 comprising silicon substrate. The insulating effect isobtained in particular by means of the silicon nitride and silicon oxidelayers 7 and 6, the silicon substrate 5 essentially serving only as acarrier material. Conductive metal pads 20 for making contact with theLED are situated on the insulating layer 7.

Since silicon layers can be applied in extremely thin fashion and have agood thermal conductivity, these layers 6 and 7 are ideal for theelectrical insulation of and the dissipation of heat from theoptoelectronic components 1 via the carrier substrates 2 to the metalcarrier 4.

Arranged between the carrier substrates 2 are printed circuit boards 8serving for electrically interconnecting the optoelectronic components1. A wiring 9 is provided for the connection between the printed circuitboards 8 and the optoelectronic components 1.

In order to be able to pot the LEDs and also for the purpose ofproducing a reflector, a frame 10 is placed onto the light sourcemodule, which frame in each case encloses a carrier substrate 2 withemplaced optoelectronic components 1.

The frame 10 is adhesively bonded at the underside to the printedcircuit boards 8, thereby enabling the interspaces in which the LEDs aresituated to be potted.

In order to obtain a reflector, the frame is first potted withreflective potting composition 11, such as e.g. white silicone or afilling composition with titanium oxide (TiO₂) or else an epoxy resinadmixed with titanium oxide particles.

The potting is effected to just under the upper edge of the carriersubstrate 2, the surface of the reflective potting composition 11running concavely to the inner edge of the frame 10.

In the second step, the interior space is potted with clear pottingcomposition 12, transparent silicone or transparent epoxy resingenerally being used for this purpose.

As a result of the frame 10 being potted with the reflective and clearpotting composition 11 and 12, said frame is connected more or lessfixedly to the LEDs.

The frame 10 is generally produced from plastic for cost reasons, thusresulting in large loads with regard to the LEDs in the event of greattemperature differences, since the plastic frame 10 expands differentlythan the metal carrier 4 that is generally composed of aluminum.

In order to absorb these mechanical loads on the LEDs, expansion joints13 are provided in the frame 10 and can be used to absorb the greatlytemperature-dependent expansion of the metal carrier 4 made of aluminum.The expansion joints 13 may be formed as a greatly tapered location inthe frame 10, so that, at this greatly tapered location, the plastic ofthe frame 10 can deform elastically under the occurrence of loading.

The expansion joints 13, as illustrated in FIG. 1, may likewise also beformed as a complete separation of the frame 10 at this location. In thecase of the complete separation of the frame 10, a separating cut 13 ais generally provided in the expansion joint 13, thereby producingseparate frame parts 10 a and 10 b.

FIG. 2 shows in a view from above the complete frame 10 such as is usede.g. for a light source module for a head-up display system (HUD system)in a motor vehicle.

The frame 10 has thirty-two cutouts 14 in each of which a carriersubstrate 2 with at least two optoelectronic components 1, asillustrated in FIG. 1, are arranged.

For the head-up display system, for this purpose the light spots arearranged in a grid of 4.5 mm in eight columns and four rows.Polychromatic light spots are obtained by arranging a plurality ofoptoelectronic components 1 with different colors on a carrier substrate2.

In order to avoid the possible damage to the LEDs due to greattemperature fluctuations and the resulting different expansions of theframe 10 and of the metal carrier 4, the expansion joints 13 arearranged in latticed fashion in the frame 10, so that the frame issubdivided into a plurality of segments by the latticed expansion joints13. A frame segment in this case comprises a maximum of four cutouts 14.

FIG. 3 shows the section A-A from FIG. 1 through the frame 10. The frame10 is formed essentially in planar fashion and has pins 15 at itsunderside by means of which it can be mounted onto the metal carrier 4.Furthermore, mounting holes 16 are likewise provided which can likewisebe used for fitting with the metal carrier.

The cutouts 14 are illustrated in cross section in the right-hand partof the section illustrated in FIG. 3, said cutouts having smallundercuts 17 at the underside, so that the reflective pottingcomposition 11 is also taken up in a positively locking manner.

At the locations of the expansion joints 13, the frame has a trapezoidalcutout on both sides, which results in forming a thin portion (“web”) ofthe frame. This thin portion can be easily bent or deformed and can,thereby, compensate for deformations. As in FIG. 1, the remaining web issevered by means of a separating cut 13 a at this location using asawing device.

The severing may be effected after the mounting of the frame onto themetal carrier 4 has been concluded and also after the potting of thecutouts 14.

The mounting of the frame 10 is schematically illustrated briefly inFIGS. 4 to 6. FIGS. 4A to 6A in each case show the view from above, andFIGS. 4B to 6B show the side view.

FIGS. 4A and 4B show the frames described in FIGS. 2 and 3, and FIGS. 5Aand 5B show the metal carrier 4 with a flexible printed circuit board 18arranged thereon with a flexible conductor connection 19. The carriersubstrates 2 and also the optoelectronic components 1 are applied on theflexible printed circuit board 18.

FIGS. 6A and 6B show how the frame 10 is merely plugged onto the metalcarrier 4 with the flexible printed circuit board 18 already applied andis adhesively bonded to the latter.

The severing of the expansion joints 13 by means of the sawing devicemay be effected just after this method step or else not until after thepotting of the cutouts 14.

The circuit board 18 differs from circuit board 8 of FIG. 1 in thatcircuit board 18 is a flexible circuit board. Furthermore, in theembodiment shown in FIG. 5A carrier substrate 2 and components 1 arearranged on the flexible circuit board 18 whereas in FIG. 1 carriersubstrate 2 is directly applied on metal carrier 4.

The scope of protection of the invention is not restricted by thedescription of the invention on the basis of the exemplary embodiments.Rather, the invention encompasses any new feature and also anycombination of features, which in particular comprises any combinationof features in the patent claims, even if this combination is notspecified explicitly in the patent claims.

1. A light source module, comprising: a metal carrier, a plurality of LEDs connected to the metal carrier in an insulating manner, a frame surrounding the plurality of LEDs, the frame comprising expansion joints, the expansion joints each comprising a separation cut, potting composition arranged between the frame and the plurality of LEDs, and a printed circuit board disposed between the frame and the metal carrier for electrically connecting the plurality of LEDs, the printed circuit board being arranged to cover portions of the metal carrier; wherein the plurality of LEDs are connected to the metal carrier on regions of the metal carrier that are not covered by the printed circuit board.
 2. The light source module as claimed in claim 1, wherein the frame is segmented into a plurality of frame parts by the expansion joints.
 3. The light source module as claimed in claim 2, wherein a maximum of four cutouts for receiving LEDs are provided per each of the frame parts.
 4. A method for producing a light source module as claimed in claim 2, wherein the segmentation of the frame is carried out by means of a sawing device, so that separating cuts arise between the frame parts.
 5. The light source module as claimed in claim 1, wherein the frame is produced from plastic.
 6. The light source module as claimed in claim 1, wherein the frame is adhesively bonded at the underside toward the printed circuit board.
 7. The light source module as claimed in claim 1, wherein the metal carrier is produced from aluminum or copper.
 8. The light source module as claimed in claim 1, wherein the LEDs are arranged in a grid.
 9. The light source module as claimed in claim 1, wherein the printed circuit board is a flexible printed circuit board.
 10. The light source module as claimed in claim 1, wherein two LEDs are separated from each other by said frame, and the two LEDs are electrically interconnected by said printed circuit board.
 11. The light source module as claimed in claim 10, wherein each LED comprises several optoelectronic components arranged on a carrier substrate.
 12. The light source module as claimed in claim 11, wherein said printed circuit board is arranged between said carrier substrates. 